This invention relates to apparatus and methods for preventing freezing of liquids during separation of liquids from natural gas at the well head. Natural gas at the well head contains liquids such as water and hydrocarbons which are removed from the natural gas by a preliminary separator apparatus and/or a secondary dehydrator apparatus such as disclosed in my prior U.S. Pat. No. 3541763. This invention is particularly directed to preliminary separator apparatus and provides the primary function of removing liquids from the natural gas while preventing freezing of the liquids. In the past, belowground apparatus has been used which has a manually operable vent system for discharging liquids collected below ground at predetermined intervals. In addition, aboveground apparatus has been used which provides for automatic venting of liquids collected above-ground which are kept from freezing by an associated heater device. Thus, prior art separator apparatus and vent controls therefor have been located either above or below ground level.
An advantage of aboveground separator apparatus and controls is that the operator can visually inspect the apparatus to determine that the apparatus is functioning properly and accumulated liquids may be automatically removed from the apparatus. A disadvantage of aboveground equipment is that, on low volume, low pressure gas wells, the flow velocity may not be great enough to keep the flow line between the well and separator swept clean of liquids and well line freezes between the well and separator may result. An advantage of belowground apparatus is that the liquids from the well line are collected below the frost line and are not as susceptible to freezing. A disadvantage of belowground apparatus is that automation of liquid discharge is difficult, fluid levels cannot be easily determined, and the operator has difficulty in determining if the apparatus is properly functioning.
The primary object of the present invention is to provide a freeze-proof preliminary separator system having an unheated first stage underground system associated with a heated second stage aboveground system. An additional object is to provide liquid discharge means for automatic transfer of liquids collected in the underground system to the aboveground system while preventing freezing of the liquids during transfer therebetween. Another object is to provide inspection means whereby operating or maintenance personnel can easily determine if the underground system is functioning properly. Other objects and advantages will be apparent from the following general and detailed descriptions of the invention.
In general, the separator system of present invention comprises an elongated cylindrical tank of relatively long length (e.g., approximately 15 feet) and relatively small diameter (e.g., approximately 1 foot) mounted in a vertical attitude with a lowermost portion of substantial length (e.g., 4 feet) buried in the ground in the vicinity of a natural gas well head. The tank is divided into upper and lower compartments by a divider plate located a relatively short distance (e.g., approximately one foot above ground level. The lower compartment has a tank inlet opening located above the bottom of the tank and beneath the divider plate so as to be connectable to an underground natural gas pipeline located beneath the frost line for a particular geographical location of a natural gas well which supplies natural gas to the separator system. The lower compartment is connected to the aboveground upper compartment by a fluid passage in a tubular member mounted in a vertical attitude in the tank in juxtaposition to a side wall portion of the tank opposite the tank inlet opening. A gas-liquid inlet opening is provided in the lower end portion of the tubular member adjacent the bottom of the tank and a gas-liquid outlet opening is provided in the upper end portion of the tubular member a substantial distance (e.g., approximately 2 feet) above the divider plate in the upper compartment. Gas and liquids, such as water and hydrocarbons, from the well head flow into the lower compartment through the tank inlet opening and downwardly toward the bottom of the tank and the tubular gas-liquid inlet opening adjacent the bottom of the tank which provides a reservoir for the liquids. When the upper level of the liquids rises above the tubular gas-liquid inlet opening, the relatively high pressure (e.g., 100 to 150 psi) of the natural gas in the lower compartment forces liquids up the tubular member to the upper compartment which provides a second liquid reservoir at the bottom thereof above the divider plate. The liquids collected in the second liquid reservoir are automatically periodically removed from the upper compartment by actuation of a conventional float operated control means whenever the level of liquids in the upper compartment rises above a predetermined maximum level. The gas in the second compartment flows upwardly through a conventional gas-liquid separator means, such as a wire mesh mist extractor device, to provide relatively dry supply gas in the upper end portion of the upper compartment which is connected to a gas discharge line through a gas outlet opening in the tank. A housing is mounted about an intermediate aboveground portion of the tank, which includes the second liquid reservoir, and a gas operated heat generating device is associated with the housing to heat and prevent freezing of the liquids and supply gas in the second reservoir and in the upper compartment. If operation of the separator system is terminated for any reason, the liquids in the first reservoir located below the ground frost line level in the lower compartment are protected against freezing.